Under the Surface: Pond Life in Winter
By Jennifer Meikle, Environmental Educator
Have you ever looked out across a frozen pond in winter and thought about the creatures that would normally be sunning themselves or gliding through the water on a warm summer day? Have you ever wondered what they are doing when it is cold out, if they can even survive a harsh winter season? There is a lot more going on under the surface of a pond than you might think.
Turtles, frogs, and fish will take shelter under fallen leaves, rocks, and logs in the water. When the water begins to get colder, they will move to the bottom of the pond and even burrow into the mud. Reptiles and amphibians don’t hibernate, although the process is similar. When temperatures begin to drop and the length of the day shortens, aquatic reptiles and amphibians enter a state of brumation. This is when their metabolism slows down and they don’t need to eat or drink very much. They eat a lot of food before entering brumation because their body lives off their stored fat and glycogen during this time. Unlike hibernation, during brumation the animals will sometimes have short bursts of activity and swim around.
Frogs have lungs but can also breathe through their skin; they absorb dissolved oxygen through the water. When water gets cold, oxygen is more highly concentrated, which allows the frogs to breathe underwater during winter and early spring. During summer, they use their lungs to breathe air above the surface. Turtles also have lungs and breathe surface air most of the time, but during winter they primarily breathe through what is called cloacal respiration. In short, this means that they breathe through their butt! The area of a turtle’s bottom has a bunch of blood vessels that absorb oxygen from water moving across it. Their alternative form of breathing allows them to really hunker down into the mud at the bottom of the pond to keep warm.
Some plants, fish, and insects remain active even under the ice. A layer of ice can actually help protect the water from the extremes of winter weather. The temperature of the water under the ice usually stays just above freezing. However, if the layer of ice gets too thick or covered with snow for too long, it can diminish oxygen levels by preventing the plants and algae in the water from photosynthesizing and blocking off the oxygen exchange between the water and air. This can cause a “winter kill,” resulting in the death of many frogs, fish, and turtles due to lack of oxygen.
If you look closely at the ice covering a frozen pond, you might be just in time to see a creature swimming by and stretching its legs before going back to rest in the mud at the bottom.